The Neutron Dance

Caltech geochemist John Eiler aims to reveal “the genetics of everything”—the history of each molecule in the natural world as written in its isotopic structure. What he finds out could have implications for ventures ranging from the study of meteorites to medical diagnosis and treatment.

It all starts with the humble neutron.

Eiler’s investigations zero in on rare isotopes, alternative versions of familiar elements that provide a third dimension to the periodic table. Every isotope has a different number of neutrons at its heart, making it more or less massive than its cousins that form the same chemical bonds.

Much in the way each spiral of DNA encodes a biological epic, a molecule tells its story through its complicated clumps of rare isotopes.

“You can think of a sample’s isotopic profile as a fingerprint, or a record book of all of the transformations it has undergone,” says Eiler, Caltech’s Robert P. Sharp Professor of Geology and Geochemistry. “It includes information like the temperatures at which chemical reactions occurred or the extents of those reactions.”

Among the isotope’s chief interpreters, Eiler has made it possible to view the arrangement of exotic atoms as something like a time-traveling thermometer.

From a meteoric chunk of Mars, his research team read the surface temperature of the red planet from four billion years ago (mild, by Earth standards). From a dinosaur tooth, they decoded the body temperature of a beast that has been extinct for 150 million years (warm-blooded, it turns out). And by remixing mass spectrometry methods, they invented a tool that discerns the temperature at which a given sample of methane formed.

Eiler is eager to share his isotopic literacy with other scientists. Just as researchers at Caltech and elsewhere developed the techniques and tools that enabled an international collaboration to map the human genome, he and his team want to create technologies and adapt instruments from other fields to lay bare the language of the isotope.

“The purpose of my research program—if you could boil it down to one thing—is to open up this world of isotopic structural diversity so we can study it,” Eiler says. “My group is developing technologies that let you freely explore the subject, move around among the types of chemicals that you analyze. We want to take technical limitations out of the equation.”

Philanthropy has accelerated Eiler’s work, allowing him to leap ahead by following his instincts and the growing possibilities opened up by each new enhancement. His investigations have moved forward thanks to a gift from Caltech trustee Charlie Trimble (BS ’63, MS ’64) and the partnership of lab equipment maker Thermo Fisher Scientific. Early backing also came from donor funds allocated by Caltech’s provost and the chair of the Division of Geological and Planetary Sciences.

“My program of research only exists because of discretionary funding. The technical innovations can’t really be justified in advance—so you’re basically asking people to trust your vision of where this will go.”

- John Eiler

“Caltech is a community of people who trust each other to do their best,” Eiler says. “When our leaders support one of my ideas, they know I’m not guaranteeing success. I’m just going to do my best, and aim at something that’s a worthy target. And that’s enough.”

Building upon studies of dinosaur teeth and greenhouse gases, Eiler’s research group continues to pursue an inclusive—even restless—approach that crisscrosses scientific disciplines. With each new development, his team can analyze bigger, more complicated molecules using tinier samples.

And with each advance, they open up fresh areas for isotopic investigation: What can we learn about human metabolism and disease? Can chemistry yield a new type of forensics to employ at crime scenes or oil spills? How did the molecules of life themselves end up in ancient rocks and meteorites?

“These are all excellent questions, and you could say I’m passionate about all of them,” Eiler says. “But there are lots of good questions. I am happy to contribute to one and then move on to another good question. And I’m perfectly happy to move around in the fields of science. At Caltech, I feel free to do so.”